The objectives of the project are to demonstrate in a statistically valid number of patients, the clinical utility of the new technique of ELASTOGRAPHY is an adjunct diagnostic tool for the diagnosis of benign and malignant breast masses. Currently, mammography is the primary screening tool for the diagnosis of breast cancer. It is sensitive but often not very specific with approximately 75% of the masses biopsied being non-cancerous. Recently sonography has been shown to be a useful tool for distinguishing solid from cystic masses and for diagnosis solid masses. But often the sonographic features that distinguish benign form malignant masses are subtle and subjective in nature. Elastography is a technique that uses the raw ultrasound signal to produce an image of HARDNESS of breast tissue rather than the normal sonographic image of backscatter intensity. Because breast cancers have long been known to be significantly harder than normal breast tissue and benign breast masses, elastography promises to be helpful in distinguishing benign from malignant masses. Preliminary studies in over 100 patients with biopsy proven breast masses has shown that elastography can reliable identify breast cancers and can distinguish cancers from benign masses in most cases. Using a subjective index of brightness on the elastogram plus the difference in transverse dimension on a mass on elastography and sonography, 11 of 15 benign masses could be classified as definitely benign without incorrectly classifying any cancers as benign. Using these two features, the area of the ROC curve (Az) was 0.86 performance similar to the PAP smear for cervical cancer. The number of cases in the preliminary study was small and only a single observer was used. The current proposal outlines a two center unblinded level of suspicion trial that will demonstrate whether elastography plus mammography and sonography increases the diagnostic confidence of readers for breast cancer and benign masses. Also, a blinded rereading study is proposed that will demonstrate the performance of each modality alone and in conjunction with the other modalities. The number of patients to be studied (about 750) will be sufficient to estimate Az to a standard deviation of 0.02. Since elastography also may be helpful in other organs such as the thyroid, renal transplants, lymph nodes and muscles, pilot studies to evaluate the potential value of elastography in those organs are also proposed. The overall hypothesis is: Elastography is capable of differentiating normal and abnormal tissues, including cancer, in an in vivo clinical environment. The overall hypothesis is: Elastography is capable of differentiating normal and abnormal tissues, including cancer, in an in vivo clinical environment. Specific Aims of the Project are: 1. Establish and define the elastographic properties of normal and abnormal breast tissue in vivo. 2. Conduct a clinical study to explore the potential role of elastography in breast cancer diagnosis. 3. Explore in vivo elastography animal models of normal and abnormal tissues. Specific studies will include normal canine prostate, canine prostate carcinoma, and woodchuck hepatoma models. 4. Explore the application of elastography to other superficial organs in humans such as thyroid, testicles, muscles, and renal transplants.